Semiconductor device and manufacturing method thereof

ABSTRACT

There are constituted by a tab ( 1   b ) on which a semiconductor chip ( 2 ) is mounted, a sealing portion ( 3 ) formed by resin-sealing the semiconductor chip ( 2 ), a plurality of leads ( 1   a ) each having a mounted surface ( 1   d ) exposed to a peripheral portion of a rear surface ( 3   a ) of the sealing portion ( 3 ) and a sealing-portion forming surface ( 1   g ) disposed on an opposite side thereto, and a wire ( 4 ) for connecting a pad ( 2   a ) of the semiconductor chip ( 2 ) and a lead ( 1   a ), wherein the length (M) between inner ends ( 1   h ) of the sealing-portion forming surfaces ( 1   g ) of the leads ( 1   a ) disposed so as to oppose to each other is formed to be larger than the length (L) between inner ends ( 1   h ) of the mounted surfaces ( 1   d ). Thereby, a chip mounting region surrounded by the inner end ( 1   h ) of the sealing-portion forming surface ( 1   g ) of each lead ( 1   a ) can be expanded and the size of the mountable chip is increased.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 12/408,890filed Mar. 23, 2009now U.S. Pat. No. 7,843,049, which is a continuationof application Ser. No. 10/519,785 filed Sep. 6, 2005 (now U.S. Pat. No.7,525,184 issued Apr. 28, 2009), which is a 371 of International PatentApplication No. PCT/JP2003/006830 filed May 30, 2003.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a semiconductor manufacturing techniqueand particularly to a technique effectively applied to enlargement ofthe size of a chip to be mountable.

BACKGROUND OF THE INVENTION

As a semiconductor device intended to be downsized, a smallsemiconductor package slightly larger in size than a semiconductor chip,which is called a QFN (Quad Flat Non-leaded Package), has been developedand the semiconductor package, having such a structure that a pluralityof leads to be external terminals are disposed on a peripheral portionof a rear face of a sealing portion formed by a resin mold, is called aperipheral type.

In the QFN, since the respective leads are exposed to the rear face ofthe sealing portion, bonding regions between the respective leads and asealing resin are very small, so that various devices for increasing abonding strength between each lead and the sealing portion have beenmade.

Note that the structure of the QFN is described in, for example,“Monthly Semiconductor World Special Edition '99, SemiconductorAssembly/Inspection Technology”, pp. 53-57, published by KabushikiKaisha Press Journal, on Jul. 27, 1998.

In the QFN, as shown in a comparative example of FIG. 14, the extendinglength (P) of a mounted surface 1 d, which is exposed to a rear surface3 a of a sealing portion 3 of each lead 1 a and functions as an externalterminal, has the relation “Q≧P” in comparison with the length (Q) of asealing-portion forming surface 1 g that is located on an opposite sidethereof and covered with a resin sealing portion.

This is because, on a sealing-portion forming surface 1 g of each lead 1a, there are formed a plurality of concave portions 1 m, which preventsexertion of a stress to a wire bonding portion at a time of cutting thelead and increases a pulling strength of each lead with respect to ahorizontal direction, whereby the length (Q) of the sealing-portionforming surface 1 g is larger and consequently the relation “Q≧P” isformed.

When it is intended to mount a larger semiconductor chip withoutchanging the package size in accordance with demands etc. from acustomer under the above condition, the extending length (P) of themounted surface 1 d cannot be shortened in view of the fixed packagesize since the length (P) is defined per package size based on EIJAstandards (Standards of Electronic Industries Association of Japan).

Accordingly, it becomes a problem that mounting of the largersemiconductor chip cannot be achieved without changing the package size.

An object of the present invention is to provide a semiconductor devicein which mountable chip size is increased and to provide a manufacturingmethod thereof.

The above and other objects and novel features of the present inventionwill become apparent from a description of the specification and theaccompanying drawings.

DISCLOSURE OF THE INVENTION

That is, the present invention comprises: a tab on which a semiconductorchip is mounted; a sealing portion for sealing said semiconductor chip;a plurality of leads each having a mounted surface exposed to aperipheral portion of a rear surface of said sealing portion, and asealing-portion forming surface disposed on an opposite side to themounted surface and contacting with a side surface of said sealingportion; and a plurality of wires for connecting surface electrodes ofsaid semiconductor chip and said leads corresponding thereto, wherein alength between inner ends of said sealing-portion forming surfaces ofsaid leads disposed to oppose to each other is longer than a lengthbetween inner ends of said mounted surfaces.

Also, the present invention comprises the steps of: preparing a leadframe having a tab capable of supporting a semiconductor chip and aplurality of leads disposed around said tab, wherein a length betweeninner ends of sealing-portion forming surfaces of said leads disposed tooppose to each other is larger than a length between inner ends ofmounted faces located on an opposite side thereto; disposing saidsemiconductor chip within a region surrounded by an inner end of saidsealing-portion forming surface of each of said plurality of leads, andthereafter mounting said semiconductor chip on said tab; connectingsurface electrodes of said semiconductor chip and said leadscorresponding thereto by wires; forming a sealing portion that themounted surfaces of said plurality of leads are exposed to and arrangedon a peripheral portion of a rear surface by resin-sealing saidsemiconductor chip and said wire; and cutting each of said leads andseparating it from said lead frame.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing one example of a frame structure as seenthrough a sealing portion in a structure of a semiconductor device (QFN)according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing the structure of the QFN shown inFIG. 1.

FIG. 3 is an enlarged partial bottom view showing a lead structure of alead frame used for assembly of the QFN shown in FIG. 1.

FIG. 4 is an enlarged partial plan view of the lead shown in FIG. 3.

FIG. 5 is an enlarged partial sectional view of the lead shown in FIG.3.

FIG. 6 is a sectional view taken along line A-A of the lead shown inFIG. 4.

FIG. 7 is a partial plan view showing one example of a structure of alead frame used for assembly of the QFN shown in FIG. 1.

FIG. 8 is a plan view showing a frame structure as seen through asealing portion in a semiconductor device (QFN) that is a modifiedexample of a first embodiment of the present invention.

FIG. 9 is a sectional view showing the structure of the QFN shown inFIG. 8.

FIG. 10 is an enlarged partial bottom view showing a lead structure of alead frame used for assembly of the QFN shown in FIG. 8.

FIG. 11 is an enlarged partial plan view of the lead shown in FIG. 10.

FIG. 12 is an enlarged partial sectional view of the lead shown in FIG.11.

FIG. 13 is a partial side view showing one example of a gap between asemiconductor chip and a capillary at a time of wire bonding in assemblyof the QFN shown in FIG. 8.

FIG. 14 is a sectional view showing a structure of a QFN, which is acomparative example with respect to a QFN according to a firstembodiment of the present invention.

FIG. 15 is a plan view showing one example of a flow state of a sealingresin in a QFN according to a second embodiment of the presentinvention.

FIG. 16 is a sectional view showing the structure of the QFN shown inFIG. 15.

FIG. 17 is a sectional view showing a structure of a semiconductordevice (QFN) that is a modified example of a second embodiment of thepresent invention.

FIG. 18 is an enlarged partial bottom view showing a lead structure of alead frame used for assembly of the QFN shown in FIG. 15.

FIG. 19 is an enlarged partial plan view of the lead shown in FIG. 18.

FIG. 20 is an enlarged partial sectional view of the lead shown in FIG.18.

FIG. 21 is a sectional view taken along line J-J of the lead shown inFIG. 19.

FIG. 22 is a sectional view taken along line B-B of the lead shown inFIG. 19.

FIG. 23, FIG. 26, FIG. 29, and FIG. 32 are enlarged partial bottom viewsshowing a lead structure of a modified example of a second embodiment ofthe present invention.

FIG. 24, FIG. 27, FIG. 30 and FIG. 33 are enlarged partial plan views ofrespective leads.

FIG. 25, FIG. 28, FIG. 31 and FIG. 34 are enlarged sectional views ofrespective leads.

FIG. 35 is a manufacturing process flow diagram showing one example ofan assembly procedure for the GFN (single-piece molding type) shown inFIG. 15.

FIG. 36 is an enlarged partial sectional view showing one example of astructure at a time of wire bonding in the procedure shown in FIG. 35.

FIG. 37 is a manufacturing process flow diagram showing a procedure forassembly of a modified example (batch molding type) of a secondembodiment of the present invention.

FIG. 38 is a partial sectional view and an enlarged partial sectionalview which show one example of a structure at a time of resin molding ina procedure for the assemble shown in FIG. 37.

FIG. 39 is a plan view showing, through a sealing portion, one exampleof a structure of a QFN according to a third embodiment of the presentinvention.

FIG. 40 is a sectional view showing the structure of the QFN shown inFIG. 39.

FIG. 41 is a plan view showing, through a sealing portion, a structureof a QFN that is a modified example of a third embodiment of the presentinvention.

FIG. 42 is a sectional view showing the structure of the QFN shown inFIG. 41.

FIG. 43 is an enlarged partial sectional view showing a structure of theC portion shown in FIG. 42.

FIG. 44 is a plan view showing, through a sealing portion, one exampleof a structure of a QFN according to a fourth embodiment of the presentinvention.

FIG. 45 is a sectional view showing a structure taken along the line D-Dof FIG. 44.

FIG. 46 is a partial plan view showing, through a sealing portion, oneexample of a structure obtained after resin molding in assembly of theQFN shown in FIG. 44.

FIG. 47 is a partial sectional view showing a structure taken along theline E-E of FIG. 46.

FIG. 48 is a plan view showing, through a sealing portion, a structureof a QFN that is a modified example of a fourth embodiment of thepresent invention.

FIG. 49 is a sectional view showing a shape taken along the line F-F ofFIG. 48.

FIG. 50 is a plan view showing, through a sealing portion, a structureof a QFN that is a modified example of a fourth embodiment of thepresent invention.

FIG. 51 is a sectional view showing a structure taken along the line G-Gof FIG. 50.

FIG. 52 is an enlarged partial plan view showing one example of arelation between a mounted surface of each lead and a terminal of amounting substrate in a structure for mounting, on the substrate, a QFNaccording to a fourth embodiment of the present.

FIG. 53 is an enlarged partial sectional view showing a connecting stateof a lead and a terminal on a substrate in the mounting structure shownin FIG. 52.

FIG. 54 is a plan view showing, through a sealing portion, one exampleof a state at a time of an electric characteristic inspection executedafter assembly of a QFN according to a fourth embodiment of the presentinvention.

FIG. 55 is a sectional view showing a structure taken along the line H-Hof FIG. 54.

FIG. 56 is a sectional view showing one example of a socket mountingstate at a time of an electric characteristic inspection executed afterassembly of a QFN according to a fourth embodiment of the presentinvention.

FIG. 57 is an enlarged partial sectional view showing a structure of the“I portion” shown in FIG. 56.

FIG. 58 is a partial plan view showing one example of a supply state ofa GND potential at a time of the electric characteristic inspectionshown in FIG. 56.

FIG. 59 is a plan view showing, through a sealing portion, one exampleof structure of a QFN according to a fifth embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be detailed basedon the drawings.

In the following embodiments, the invention will be described in aplurality of sections or embodiments when required as a matter ofconvenience. However, these sections or embodiments are not irrelevantto each other unless otherwise stated, and the one relates to the entireor a part of the other as a modification example, details, asupplementary explanation or the like thereof.

Also, in the embodiments described below, when referring to the numberof elements (including number of pieces, values, amounts, ranges, or thelike), the number of elements is not limited to a specific number unlessotherwise stated, or except the case where the number is apparentlylimited to a specific number in principle, or the like. The numberlarger or smaller than the specified number is also applicable.

Note that, throughout all the drawings for describing the embodiments,members having the same function are denoted by the same referencenumeral and a repetitive description thereof will be omitted.

First Embodiment

A semiconductor device according to a first embodiment shown in FIGS. 1and 2 is a small semiconductor package, which is assembled using a leadframe shown in FIG. 7 and is a single-surface-molding resin sealing typein which a sealing portion 3 is formed on a single-surface side of alead frame 1 by resin molding, and it is further a peripheral type inwhich mounted surfaces 1 d of a plurality of leads 1 a are exposed toand arranged on a peripheral portion of a rear surface 3 a of thesealing portion 3, and, as an example of said semiconductor device, aQFN 5 is taken and will be described.

Therefore, each lead 1 a of the QFN5 functions as both an inner leadembedded in the sealing portion 3 and an outer lead exposed to theperipheral portion of the rear surface 3 a of the sealing portion 3.

Note that, in the QFN 5 shown in FIG. 2, a tab 1 b, which is a chipmounting portion, is formed to have about half thickness of that of thelead 1 a since its rear surface 1 l is scraped by a process such as halfetching, and thereby a sealing resin flows also on a side of the rearsurface 1 l of the tab 1 b and resin molding is made. That is, althoughthe QFN 5 has a tab embedding structure in which the tab 1 b is embeddedin the sealing portion 3, it may have a tab exposing structure in whichthe rear surface 1 l of the tab 1 b is exposed to a rear surface 3 a ofthe sealing portion 3.

Further, although the QFN 5 has a tab structure in which the tab 1 b issmaller in size than the semiconductor chip 2, the QFN 5 is not limitedto the above small tab structure and may have a structure in which thetab 1 b is equal to or larger than the semiconductor chip 2 in size.

The structure of the QFN 5 shown in FIGS. 1 and 2 will be described. Itcomprises: a tab 1 b that has a chip supporting surface 1 c forsupporting the semiconductor chip 2 and in which the semiconductor chip2 is mounted on the chip supporting surface 1 c; a sealing portion 3formed by resin-sealing the semiconductor chip 2; a tab hanging lead 1 efor supporting the tab 1 b; a plurality of leads 1 a each having themounded surface 1 d exposed to the peripheral portion of the rearsurface 3 a of the sealing portion 3 and the sealing-portion formingsurface 1 g disposed on an opposite side thereof and contacting with aside surface 3 b of the sealing portion 3; and a plurality of wires 4connecting pads 2 a serving as surface electrodes of the semiconductorchip 2 and the leads 1 a corresponding thereto, wherein it is formed sothat the length (M) between inner ends 1 h of the sealing-portionforming faces 1 g of the leads 1 a disposed to oppose each other amongthe plurality of leads 1 a is larger than the length (L) between innerends of the mounted surfaces 1 d.

That is, as shown in FIG. 2, the respective leads 1 a are formed so thatthe length (M)>the length (L) between the leads 1 a opposed to eachother.

Further, the respective leads 1 a are such that “the length (Q) of thesealing-portion forming surface 1 g”<“the length (P) of the mountedsurface id” is formed.

Therefore, it is possible to expand each chip mounting region surroundedand formed by the inner ends 1 h of the sealing-portion forming surfaces1 g of the respective leads 1 a and consequently to achieve enlargementof the mountable chip size without changing the package size.

Therefore, the larger semiconductor chip 2 can be mounted.

Here, the maximum values of the mountable chip size are compared betweenthe QFN 5 according to the first embodiment shown in FIG. 2 and a QFNtype semiconductor device that is a comparative example shown in FIG.14. Firstly, in the QFN type semiconductor device that is thecomparative example shown in FIG. 14, if it is assumed that the length(L) between the inner ends 1 h of the mounted surfaces 1 d of the leads1 a disposed to oppose to each other is 3 mm, the length (M) between theinner ends 1 h of the sealing-portion forming surfaces 1 g is 2.9 mm. Inview of mounting accuracy of a die bonder, a margin of 0.1 mm from anedge of the semiconductor chip 2 is necessary and the maximum value (N)of the mountable chip size becomes 2.7 mm (2.7 mm×2.7 mm) by calculating“the length (M)−0.2 mm”.

In contrast, in the case of the QFN 5 of the present embodiment shown inFIG. 2, if it is assumed that the package size is the same and thelength (L) between the inner ends 1 h of the mounted surfaces 1 d of theleads 1 a disposed to oppose to each other is similarly 3 mm, the length(M) between the inner ends 1 h of the sealing-portion forming surfaces 1g is 3.2 mm. Consequently, the maximum value (N) of the mountable chipsize becomes 3.0 mm (3.0 mm×3.0 mm).

Thus, even if the package size is the same, the QFN 5 shown in FIG. 2 inthe present embodiment can mount the semiconductor chip 2 larger in sizethan the QFN type semiconductor device that is the comparative exampleshown in FIG. 14.

Also, in the QFN 5 of the present embodiment shown in FIG. 2, since thechip mounting region surrounded and formed by the inner ends 1 h of thesealing-portion forming surfaces 1 g of the respective leads 1 a can beexpanded, the bonding accuracy at a time of die bonding can be reduced.

Further, the inner ends 1 h on sides of the sealing-portion formingsurfaces 1 g of the leads 1 a are located more apart from thesemiconductor 2 than the inner ends 1 h on sides of the mounted surfaces1 d. Therefore, in the case of mounting the large semiconductor chip 2,even if a vertical deviation of the chip occurs due to resin injectionpressure, it is possible to prevent the leads 1 a and the semiconductorchip 2 from contacting with one another and to reduce damage to thechip.

Note that, in the QFN 5 shown in FIG. 2, as shown in FIGS. 4 and 5, oneconcave portion 1 m is formed in a region that is outside a bondingpoint 1 f and inside a molding line 1 k of each lead 1 a.

This concave portion 1 m is a place to which, when a stress occurring ata time of cutting out the lead during a lead cutting process is exertedon the lead 1 a, the stress is applied. Since the concave portion 1 m isformed, the stress can be prevented from being applied to a wire bondingportion and disconnection of the wires 4 can be prevented at a time ofcutting out the lead 1 a.

Further, since the concave portion 1 m is formed, the pulling strengthof the lead 1 a with respect to a horizontal direction of the packagecan be improved.

Also, in the QFN 5 shown in FIG. 2, as shown in FIGS. 3, 4, and 6, atleast one portion of the sealing-portion forming surface 1 g is formedlarger in width than the mounted face 1 d. That is, as shown in FIG. 6,the sealing-portion forming surface 1 g formed on an upper side isformed larger in width than the mounted surface 1 d disposed on a lowerside and the lead is formed into an inverted trapezoidal shape in athickness direction thereof.

Thereby, a pulling strength of the lead 1 a in a package-verticaldirection can be improved.

Also, as shown in FIG. 2, the semiconductor chip 2 is fixed on the chipsupporting surface 1 c of the tab 1 b by a die bond material (e.g.,silver paste etc.).

Further, a solder plating layer 6 having a thickness of approximately 10μm is formed on the mounted surface 1 d of each of the leads 1 a, whichare external terminals disposed in parallel on the peripheral portion ofthe rear surface 3 a of the sealing portion 3 of the QFN 5.

Also, the tab 1 b, the tab hanging lead 1 e, and the respective leads 1a are formed of thin-sheet materials of copper etc. and their thicknessis approximately 0.15 to 0.2 mm.

Further, the wires 4 for connecting the pads 2 a of the semiconductorchip 2 and the leads 1 a corresponding thereto are made of, for example,gold etc.

Also, the sealing portion 3 is formed by resin-sealing in a moldingmethod, and a sealing resin used in its formation is, for example, athermoplastic epoxy resin etc.

Next, a method of manufacturing the GFN 5 (semiconductor device)according to the first embodiment will be described.

Firstly, there is prepared a lead frame 1 shown in FIG. 7, whichcomprises the tab 1 b capable of supporting the semiconductor chip 2,the tab hanging lead 1 e for supporting the tab 1 b, and the pluralityof leads 1 a disposed around the tab 1 b, wherein the length between theinner ends 1 h of the sealing-portion forming surfaces 1 g of the leads1 a disposed to oppose to each other is formed larger than the lengthbetween the inner ends 1 h of the mounted surfaces 1 d.

That is, as shown in FIG. 2, there is prepared the lead frame 1 in whichthe respective leads 1 a are such that “the length (Q) of eachsealing-portion forming surface 1 g”<“the length (P) of the mountedsurface 1 d” is formed.

Also, as shown in FIG. 7, cutting portions for sectioning the tab 1 band the leads 1 a disposed on a periphery thereof are formed on the leadframe 1. Note that dotted lines in FIG. 7 indicate mold lines 1 k aftermolding.

Further, the lead frame 1 is a strip-shaped multiple one capable ofmanufacturing the plurality of QFNs 5 from one sheet of lead frame 1.Further, the QFNs 5 can be manufactured in matrix arrangement on onesheet of lead frame 1. Thus, a plurality of package regions, each ofwhich corresponds to one QFN 5, are formed in matrix arrangement on onesheet of lead frame 1.

Also, the lead frame 1 is made of, for example, a thin-sheet material ofcopper (Cu) etc. and its thickness is approximately 0.15 to 0.2 mm.However, the above-mentioned material and the above-mentioned thickness,etc. are not limited to this example.

Thereafter, the semiconductor chip 2 in which a semiconductor integratedcircuit is formed on a main surface 2 a thereof is prepared, and thesemiconductor chip 2 is disposed on the tab 1 b within a regionsurrounded by the inner end 1 h of each sealing-portion forming surface1 g of the plurality of leads 1 a.

Thereafter, die bonding (called also pellet bonding or chip mounting)for joining the rear surface 2 c of this semiconductor chip 2 and thechip supporting surface 1 c of the tab 1 b is performed.

That is, the semiconductor chip 2 is mounted on the chip supportingsurface 1 c of the tab 1 b of the lead frame 1.

At this time, the semiconductor chip 2 is fixed to the tab 1 b of thelead frame 1 through a die bonding material (e.g., silver paste etc.) sothat the main surface 2 b is faced upward.

Subsequently, as shown in FIG. 2, the pad 2 a of the semiconductor chip2 is connected, by wire bonding that utilizes the wire 4 for bonding, toa vicinity of the bonding point 1 f on the sealing-portion forming face1 g of the lead 1 a which is shown in FIG. 4 and corresponds to theabove pad.

Thereafter, the semiconductor chip 2 and the plurality of wires 4 areresin-sealed by the resin molding (in this case, transfer molding) toform the sealing portion 3 on a side of the sealing-portion formingsurface 1 g of the lead frame 1 (single-surface molding is carried out).

At this time, the resin molding is executed so that the mounted faces 1d of the plurality of leads 1 a are exposed to and arranged on theperipheral portion of the rear surface 3 a of the sealing portion 3.

In this case, the resin molding is carried out using a molding die 8 ofa single-piece molding type, in which a cavity 8 c of the molding die 8(see FIG. 35) corresponds to the QFN 5 one to one.

Consequently, the plurality of sealing portions 3 are formed on the leadframe 1 in matrix arrangement.

Thereafter, there is performed lead cutting (separation to individualpieces) in which the respective leads 1 a and tab hanging leads 1 eprojecting from the sealing portion 3 are cut out and separated from thelead frame 1.

In this case, the respective leads 1 a are cut out along the cuttingportion 1 j of the lead frame 1 to obtain the QFN 5 shown in FIG. 2.

Next, a QFN 5 that is a modified example of the first embodiment will bedescribed.

FIGS. 8 and 9 show the QFN 5 that is the modified example and also FIGS.10 to 12 show the shape of each lead 1 a of the QFN 5 that is themodified example.

That is, although the QFN 5 shown in FIGS. 8 and 9 has substantially thesame structure as the QFN 5 shown in FIG. 2, a difference between themis the shape of the sealing-portion forming surface 1 g of each lead 1 aand is the point that a notch portion 1 l as shown in FIG. 12 is formedin the inner end 1 h of the sealing-portion forming surface 1 g of eachlead 1 a.

That is, the notch portion 1 i having a step portion which is lower inheight than the sealing-portion forming surface 1 g is provided in aninner corner portion of the sealing-portion forming surface 1 g of eachlead 1 a.

By providing this notch portion 1 i, the length (M) between the innerends 1 h of the sealing-portion forming surfaces 1 g of the leads 1 adisposed to oppose to each other is larger than the length (L) betweenthe inner ends 1 h of the mounted surfaces 1 d, and, similarly to theQFN 5 shown in FIG. 2, each lead 1 a is such that “the length (Q) of thesealing-portion forming surface 1 g”<“the length (P) of the mountedsurface 1 d”.

Note that, in the QFN 5 that is a modified example shown in FIG. 9, thewire 4 is connected to the notch portion 1 i which is lowered one stepfrom the sealing-portion forming surface 1 g of each lead 1 a.

Therefore, as shown in FIG. 13, it is necessary to set size of amountable chip in view of an interval (Q) between an end portion of thesemiconductor chip 2 and a capillary 7 serving as a bonding tool so thatthe capillary 7 can enter the notch portion 1 i of the lead 1 a at thetime of wire bonding.

For example, by making the QFN 5 shown in FIG. 2 coincide with thepackage size and in view of the above-mentioned interval (Q) (e.g.,Q=approximately 0.05 mm), the mountable size is calculated. Firstly, asshown in FIG. 9, if the length (L) between the inner ends 1 h of themounted surfaces 1 d of the respective leads 1 a disposed to oppose toeach other is set to 3 mm similarly thereto, the length (M) between theinner ends 1 h of the sealing-portion forming surfaces 1 g is 3.84. Inview of mounting accuracy of the die bonder and bondability of the wirebonding, for example, a margin of 0.32 mm from the edge of thesemiconductor chip 2 is necessary and the maximum value (N) of themountable chip size becomes 3.2 mm (3.2 mm×3.2 mm) by calculating “thelength (M)−0.64”.

In this case, since the notch portion 1 i is formed in each inner end 1h of the sealing-portion forming surfaces 1 g of the leads 1 a, thesemiconductor chip 2 much larger in size than the QFN 5 shown in FIG. 2can be mounted.

Note that since the other structure and assembly method and the otheroperation and effects of the modified example shown in FIG. 9 are thesame as those of the QFN 5 shown in FIG. 2, the duplicated descriptionthereof is omitted.

Second Embodiment

In a second embodiment, a QFN 9 having substantially the same structureas the QFN 5 described in the first embodiment will be described.

FIG. 15 shows a QFN 9 having a small tab structure in which the tab 1 bshown in FIG. 16 is formed smaller in size than the main surface 2 b ofthe semiconductor chip 2 and a tab embedding structure in which aportion of the sealing portion 3 is disposed on a side of the rearsurface 1 l of the tab 1 b, wherein there is shown a flow condition of aresin (sealing resin) at a time of assembly of the QFN 9. That is, whenthe chip size increases, it becomes difficult for the sealing resin toenter a region between a side surface of the tab 1 b and each lead 1 aon a side of the rear surface 2 c of the semiconductor chip 2, in theQFN 9 of the second embodiment. However, in the QFN 9 of the secondembodiment, as shown in FIG. 16, the rear surface 1 l of the tab 1 b isprocessed to become thin by half etching etc., so that the sealing resinis made to intrude also into the side of the rear surface 1 l of the tab1 b at a time of the resin molding.

Therefore, the sealing resin flows along resin flow directions shown inFIG. 15 on the side of the rear surface 1 l of the tab 1 b and,consequently, it is possible to introduce the sealing resin around andinto the region between the side surface of the tab 1 b and each lead 1a on the rear surface of the chip and to prevent voids from occurring inthe above-mentioned region.

Note that as a processing method of thinning the rear surface 1 l of thetab 1 b, a coining method may be adopted. Also, in the QFN 9 shown inFIGS. 15 and 16, since a tab raising process is not performed, the chipsupporting face 1 c, which is a surface for mounting the chip on the tab1 b, is disposed to have the same height as the sealing-portion formingsurface 1 g of each lead 1 a.

Next, the QFN 9 that is a modified example shown in FIG. 17 has a tabembedding structure in which the tab raising process is performed andthe chip supporting surface 1 c of the tab 1 b is disposed at a positionmore apart from a direction of a main-surface side of the chip than thesealing-portion forming surface 1 g of each lead 1 a. Also in this case,similarly to the QFN 9 shown in FIG. 15, since the sealing resin flowsalong the resin flow direction on a side of the rear surface 1 l of thetab 1 b, it is possible to introduce the sealing resin around and into aregion between a side surface of the tab 1 b and each lead 1 a on therear surface of the chip and to prevent voids from occurring in theabove-mentioned region.

Thus, in the QFN 9 mounted on the semiconductor chip 2 having such largesize that an end portion of the chip approaches the leads 1 a, thinningthe tab 1 b and performing the tab raising process are effective forreducing the voids formed on the side surface of the tab 1 b in the rearsurface of the chip.

Next, the shape of leads in a QFN 9 according to a second embodimentwill be described.

Each lead 1 a shown in FIGS. 18 to 20 has the same shape as that of eachlead 1 a of the QFN 5 according to the first embodiment, wherein thereis formed the concave portion 1 m, which is one dent, outside thebonding point if corresponding to a wire joining point on thesealing-portion forming surface 1 g. This concave portion 1 m is astress reducing means for reducing a stress applied to the wire joiningpoint of each lead 1 a at a time of cutting out the leads after theresin molding so that the above stress is concentrated on the concaveportion 1 m located outside the wire joining point to avoid applying thestress to the wire joining point located inside the concave portion 1 m.Accordingly, wire peeling and/or wire cutting can be prevented fromoccurring.

Note that a single concave portion 1 m is preferably formed in thesealing-portion forming surface 1 g of each lead 1 a. That is because aperiphery of the bonding point 1 f in the sealing-portion formingsurface 1 g must be ensured as a bonding region and, if it is intendedto form the plurality of concave portions lm except the bonding region,it becomes difficult to form the respective concave portions 1 msufficiently deeply. The concave portion 1 m is such that as their depthshallows, a bonding force between the sealing resin and the concaveportion 1 m weakens and also an operation of stress relaxationdecreases.

Also, if it is intended to form the concave portion 1 m deeply, thewidth of the concave portion 1 m must be ensured to some extent in theprocess and it is very difficult to ensure a region for two concaveportions among regions other than the bonding region on thesealing-portion forming surface 1 g.

Further, in the wire bonding for the QFN 9, as shown in FIG. 36, a firstbonding is carried out on a semiconductor chip side and a second bondingis carried out on a lead side. At that time, similarly to the firstbonding, the second bonding requires an area wider than an area for thefirst bonding because the wire 4 is crushed and cut out to be connectedto each lead 1 a unlike a method of pressing and connecting a ball ofgold wire (wire 4).

Therefore, in order to obtain a sufficient effect of stress relaxation,it is preferable to form a single concave portion 1 m in a single lead 1a.

Next, in each lead 1 a of the QFN 9, the concave portion 1 m having asmaller width than that of the sealing-portion forming surface 1 g isformed in the sealing-portion forming surface 1 g with respect to adirection perpendicular to the extension direction of each lead 1 a.That is, the concave portion 1 m does not reach both side surfaces ofeach lead 1 a and terminates within the sealing-portion forming surface1 g. As shown in FIG. 19, end heavy-walled portions 1 n are formed onboth ends in the width direction of the lead 1 a of the concave portion1 m.

Since the end heavy-walled portions 1 n are formed on both ends in thewidth direction of the lead of the concave portion 1 m, it is possibleto prevent deformation of each lead 1 a at the time of the resin moldingby ensuring the strength of each lead 1 a.

That is, when the resin molding using a film 1 l as shown in FIG. 38 isadopted in a resin molding process for assembling the QFN 9, the film 1l is under each lead and each lead 1 a is inserted into the film 1 l bya clamp of a molding die 8 in order that the sealing resin is not madeto intrude into the mounted surface 1 d of each lead 1 a. Then, underthis state, the resin molding is carried out.

At this time, if the strength of each lead 1 a is weak, there arises thedrawback that the lead 1 a is deformed by a reaction force exerted at atime of clamping the molding die 8. However, similarly to the lead shapeshown in FIG. 19, since the end heavy-walled portions 1 n are formed onboth ends toward the lead-width direction of the concave portion 1 m,the strength of each lead 1 a is ensured and deformation of each lead 1a can be prevented at the time of the resin molding.

Also, as shown in FIG. 19, the lead 1 a of the QFN 9 has a wire bondingportion 1 q disposed on a chip side and a base portion 1 p sandwichedbetween the inside and the outside of the side surface 3 b of thesealing portion 3, wherein the sealing-portion forming surface 1 g inthe wire bonding portion 1 q is formed larger in width than thesealing-portion forming surface 1 g in the base portion 1 p.

That is, in the lead 1 a, the width of the sealing-portion formingsurface 1 g is different in the base portion 1 p near the outsidethereof and the wire bonding portion 1 q inside the base portion, andthe sealing-portion forming surface 1 g of the wire bonding portion 1 qlocated inside has larger width. Namely, a wide portion of thesealing-portion forming surface 1 g extends outward from the end of thechip side of each lead 1 a and terminates prior to the side surface 3 bof the sealing portion 3, thereby becoming the base portion 1 pextending from there so that the width of the sealing-portion formingsurface 1 g becomes narrow.

Consequently, the pulling strength of the lead 1 a in the extendingdirection can be intensified and thereby can prevent the lead 1 a fromdropping out of the sealing portion 3.

Also, in the wire bonding portion 1 q, the sealing-portion formingsurface 1 g is formed wider than the mounted surface 1 d disposed on anopposite side thereof, and the sectional shape of the lead 1 a in thewidth direction in the wire bonding portion 1 q is an invertedtrapezoidal shape in which its top side is longer than its bottom side,as shown in FIG. 21.

Consequently, the pulling strength of the lead 1 a in the package-widthdirection can be intensified.

Also, since the lead 1 a of the QFN 9 of a second embodiment adopts anetching process in processing its lead pattern, wherein at a time of theetching process, an etchant is applied from both sides of each of frontand rear surfaces, so that the lead 1 a is scraped from both the frontand rear side surfaces.

Thus, curved coupling portions 1 r are formed in the vicinity of acenter and in a thickness direction of each lead 1 a, in the sectionalshape of each lead shown in FIGS. 21 and 22, and the strength and thepulling strength of the lead 1 a can be improved by these curvedcoupling portions 1 r.

Note that the lead-pattern process is not limited to the etchingprocess, and may adopt a press process.

Next, the lead shapes of various kinds of modified examples shown inFIGS. 23 to 34, which are a second embodiment, will be described.

The leads 1 a shown in FIGS. 23 to 25 are equivalent to the leads 1 ashown in FIGS. 18 to 20 in terms of their external shapes. As shown inFIG. 25, the respective lengths from mold lines 1 k to chip-side ends inthe sealing-portion forming surface 1 g and the mounted surface 1 d inthe extending direction of the lead 1 a are such that “the length(R)”<“the length (P)” is formed. Further, the concave portion 1 m asshown in FIG. 19 is not formed in the sealing-portion forming surface 1g of the wire bonding portion 1 q, and the sealing-portion formingsurface 1 g is constituted only by a flat surface. This lead shape iseffective in cutting by a dicing using a blade 12 shown in FIG. 37, notin cutting by a punch, in a lead cutting process after the resinmolding.

That is, in the cutting by the dicing, since the stress applied to eachlead 1 a is smaller at a time of the lead cutting than at a time of thecutting by the punch, the damages to the wire bonding portion are alsosmall and therefore it is unnecessary to provide the concave portion 1 mthat is a stress relaxing means.

As a result, the wide bonding region can be ensured in thesealing-portion forming surface 1 g in the wire bonding portion 1 q ofeach lead 1 a, so that the second bonding can easily be performed.

Note that the case of the cutting by the dicing means the case where theresin molding is executed in batch, that is, the resin molding iscarried out with a plurality of device regions as shown in FIG. 37 arecovered with a single cavity 8 c in the molding die 8.

Next, in the lead shapes of modified examples shown in FIGS. 26 to 28,the concave portions lm are formed as stress relaxing means in both sidesurfaces of the wire bonding portion 1 q with respect to each lead 1 a.

That is, in the wire bonding portion 1 q of the lead 1 a, totally threeconcave portions 1 m, each of which comprises a concave portion 1 m inthe sealing-portion forming surface 1 g and concave portions 1 m in bothside surfaces, are formed, so that a sectional area of an outside regioncan be sufficiently made smaller than that of the bonding point 1 f inthe wire bonding portion 1 q of each lead 1 a. Therefore, the stressapplied to the bonding region at the time of cutting each lead by thepunch can be reduced sufficiently, and it is possible to preventdrawbacks such as wire peeling and wire cutting from occurring at thetime of cutting the lead by the punch.

Note that the stress relaxing means in each lead 1 a may have such ashape that the sectional area of each lead 1 a is made smaller at anoutside point than the bonding point 1 f, and may be, for example, theconcave portion 1 m, a slit, a notch, or the like.

Next, in the lead shapes of modified examples shown in FIGS. 29 to 31,the sealing-portion forming surface 1 g is set to a flat surface, andthe concave portions 1 m that are the stress relaxing means are formedon both side surfaces of the wire bonding portion 1 q with respect toeach lead 1 a.

Thus, since the concave portion 1 m is not formed and only the flatsurface exists in the sealing-portion forming surface 1 g, the widebonding region can be ensured and the stress occurring at a time ofcutting the leads can be reduced by the concave portions 1 m formed inboth side surfaces.

Also, in the lead shapes of the modified examples shown in FIGS. 32 to34, the sealing-portion forming surface 1 g is set to a flat surface andthe two concave portions 1 m each serving as the stress relaxing meansare formed on both side surfaces of the wire bonding portion 1 a withrespect to each lead 1 a.

For this reason, it is possible to ensure the wide bonding region andconcurrently reduce further the stress at a time of cutting the leads.

Next, a manufacturing method for semiconductor devices according to thesecond embodiment will be described.

Firstly, assembly of the QFN 9 of a single molding type will bedescribed with reference to FIG. 35.

As shown in step S1, there is prepared the lead frame 1, whichcomprises: the tab 1 b capable of supporting the semiconductor chip 2;the tab hanging lead 1 e for supporting the tab 1 b; and the pluralityof leads 1 a disposed around the tab 1 b and each having the mountedsurface 1 d and the sealing-portion forming surface 1 g, wherein it isformed so that the length between the inner ends 1 h of thesealing-portion forming surfaces 1 g of the leads 1 a disposed to opposeto each other is set larger than the length between the inner ends 1 hof the mounted surfaces 1 d and the concave portion 1 m serving as astress relaxing means is provided to each lead 1 a.

That is, as shown in FIG. 2, there is prepared the lead frame 1 in whicheach lead 1 a is such that “the length (Q) of each sealing-portionforming surface 1 g”<“the length (P) of the mounted surface 1 d” isformed

Note that the lead frame 1 is a stripe-shaped multiple type which canmanufacture the plurality of QFNs 9 from one sheet of lead frame 1.Further, the QFNs 9 can be manufactured in matrix arrangement on onesheet of lead frame 1 and thereby the plurality of package regions, eachof which corresponds to one QFN 9, are formed in matrix arrangement onone sheet of lead frame 1.

Thereafter, the die bonding shown in FIG. S2 is carried out.

In this step, the semiconductor chip 2 in which a semiconductorintegrated circuit is formed on a main surface 2 b is prepared, and thesemiconductor chip 2 is disposed on the tab 1 b, which is located withina region surrounded by the inner ends 1 h of the respectivesealing-portion forming surfaces 1 g of the plurality of leads 1 a.

Thereafter, the die bonding (also called pellet bonding or chipmounting) for joining the rear surface 2 c of this semiconductor chip 2and the chip supporting surface 1 c of the tab 1 b is carried out.

That is, the semiconductor chip 2 is mounted on the chip supportingsurface 1 c of the lead frame 1.

At this time, the semiconductor chip 2 is fixed to the tab 1 b of thelead frame 1 through a die bonding material (e.g., silver paste, bondingfilm (adhesive tape) or the like) so that its main surface 2 b is facedupward.

Subsequently, wire bonding shown in step S3 is carried out.

In this step, the wire bonding is carried out so that the pad 2 a of thesemiconductor chip 2 is connected, by the conductive wire 4 such as agold wire, to a vicinity of the bonding point if of the sealing-portionforming surface 1 g in a region located inside the concave portion 1 mof the lead 1 a, which corresponds to the pad and is shown in FIG. 19.

At that time, firstly, the first bonding for connecting the pad 2 a ofthe semiconductor chip 2 and the wire 4 is carried out, and then thesecond bonding for connecting the wire 4 and a vicinity of the bondingpoint if located inside the concave portion 1 m in the sealing-portionforming surface 1 g of the wire bonding portion 1 q of the lead 1 a iscarried out.

As shown in FIG. 36, the above-mentioned second bonding requires abonding region wider in area than the first bonding region since thewire 4 is crushed and cut out and connected to the lead 1 a. However, incase of the lead 1 a of the second embodiment, the second bonding regionis easy to ensure and the second bonding can be executed easily becauseonly one concave portion 1 m is formed in the sealing-portion formingsurface 1 g of the lead 1 a.

Thereafter, transfer molding is carried out in step S4. In this step,the resin molding is carried out using the molding die 8 of asingle-piece molding type in which the cavity 8 c of the molding die 8corresponds to the QFN 9 one to one.

At this time, the resin molding is carried out so that the mountedsurfaces 1 d of the plurality of leads 1 a are exposed to and arrangedon the peripheral portion of the rear surface 3 a of the sealing portion3. Consequently, by resin-sealing the semiconductor chip 2 and theplurality of wires 4, the sealing portion 3 is formed on a side of thesealing-portion forming surface 1 g of the lead frame 1 (single-surfacemolding is carried out).

Consequently, the plurality of sealing portions 3 are formed on the leadframe 1 in matrix arrangement.

Thereafter, external plating is carried out in step S5 to form asoldered plating layer 6 on the mounted surface 1 d of the lead 1 a.

Thereafter, marking in step S6 is carried out to attach a desired markto the sealing portion 3 of the QFN 9.

Then, cutting in step S7 is carried out to individuate the QFNs 9.

At that time, a portion located outside the concave portion 1 m, whichis a stress relaxing means of each lead 1 a, is clipped by a cutting die13 and each lead 1 a projecting from the sealing portion 3 is cut out bya punch to separate each lead from the lead frame 1 (separation toindividual pieces).

When the lead is cut out, the stress is concentrated to a place wherethe concave portion 1 m is formed, i.e., to a portion having thesmallest sectional area of the wire bonding portion 1 q of the lead 1 a.At that time, since the concave portion 1 m is located outside the wirebonding position of the second bonding, the stress at the time ofcutting is concentrated to the concave portion 1 m. Therefore it ispossible to prevent drawbacks such as wire peeling and wire cutting fromoccurring at a time of cutting out the leads.

Thereby, the cutting of the lead is finished, and products of the QFNs 9shown in step S8 are completed.

Next, assembly of a batch molding type QFN 9 will be described withreference to FIG. 37.

Note that, in batch sealing in which the resin molding is carried out bycovering the plurality of device regions with one cavity 8 c of themolding die 8, the lead cutting is executed by the dicing. In the caseof the lead cutting by the dicing, since the stress applied to the lead1 a at the time of cutting is smaller than that at the time of cuttingby the punch, it is also possible to adopt the sealing-portion formingsurface 1 g which has only a flat surface as shown in FIG. 24. However,the case of adopting the lead 1 a in which one concave portion 1 m isformed in the sealing-portion forming surface 1 g shown in FIG. 19 willbe described.

Firstly, as shown in step S11, there is prepared the lead frame 1comprising: the tab 1 b capable of supporting the semiconductor chip 2;the tab hanging lead 1 e for supporting the tab 1 b; the plurality ofleads 1 a disposed around the tab 1 b and each having the mountedsurface 1 d and the sealing-portion forming surface 1 g are provided,wherein the length between the inner ends 1 h of the sealing-portionforming surfaces 1 g of the leads 1 a disposed to oppose to each otheris set larger than the length between the inner ends 1 h of the mountedsurfaces 1 d and further the concave portion 1 m, which is as a stressrelaxing means and has smaller width than that of the sealing-portionforming surface 1 g, is provided on the sealing-portion forming surface1 g of each lead 1 g with respect to a direction perpendicular to theextending direction of the lead 1 a.

That is, as shown in FIG. 2, each lead 1 a is such that “the length (Q)of each sealing-portion forming surface 1 g”<“the length (P) of themounted surface 1 d” is formed, and further the lead frame 1 on whichthe end heavy-walled portion 1 n shown in FIG. 19 is formed is preparedon both ends located in the width direction of the lead of each concaveportion 1 m.

Note that the lead frame 1 is a strip-shaped multiple type which canmanufacture the plurality of QFNs 9 from one sheet of lead frame 1.Further, the QFNs 9 can be manufactured in matrix arrangement on the onesheet of lead frame 1, and thus the plurality of package regions, eachof which corresponds to one QFN 9, are formed in matrix arrangement onthe one sheet of lead frame 1.

Thereafter, the die bonding shown in step S12 is carried out.

In this step, the semiconductor chip 2, in which a semiconductorintegrated circuit is formed on its main surface 2 b, is prepared, andthe semiconductor chip 2 is disposed on the tab 1 b located within aregion surrounded by the inner end 1 h of each sealing-portion formingsurface 1 g of the plurality of leads 1 a shown in FIG. 2.

Thereafter, the die bonding (called pellet bonding or chip mounting) ofjoining the rear surface 2 c of this semiconductor chip 2 and the chipsupporting surface 1 c of the tab 1 b is carried out.

That is, the semiconductor chip 2 is mounted on the chip supportingsurface 1 c of the tab 1 b of the lead frame 1.

At that time, the semiconductor 2 is fixed on the tab 1 b of the leadframe 1 through a die bonding material (e.g., silver paste etc.) so thatits main surface 2 b is faced upward.

Subsequently, the wire bonding shown in step S13 is carried out.

In this step, the pad 2 a of the semiconductor chip 2 is connected, bythe conductive wire 4 such as a gold wire, to a vicinity of the bondingpoint if on the sealing-portion forming surface 1 g located within anrange outside the concave portion 1 m of the lead 1 a, which correspondsto the pad and is shown in FIG. 19, and thereby the wire bonding iscarried out.

At this time, firstly, the first bonding for connecting the pad 2 a ofthe semiconductor chip 2 and the wire 4 is carried out, and then thesecond bonding for connecting the wire 4 to the vicinity of the bondingpoint 1 f located inside the concave portion 1 m in the sealing-portionforming surface 1 g of the wire bonding portion 1 q of the lead 1 a iscarried out. In the case of the lead 1 a of the second embodiment, sinceonly one concave portion is formed in the sealing-portion formingsurface 1 g of the lead 1 a, the second-bonding region is easy to ensureand the second bonding can be carried out easily.

Thereafter, molding of step S14 is executed. In this step, there isperformed the batch molding in which the plurality of device regions arecovered with one cavity 8 c of the molding die 8 in a batch manner toperform the resin molding.

At that time, the resin molding is carried out in each device region sothat the mounted surfaces 1 d of the plurality of leads 1 a are exposedto and arranged on the peripheral portion of the rear surface 3 a of thesealing portion 3. At a time of the batch molding, firstly, as shown inFIG. 38, the film 1 l is disposed on a die surface of a lower die 8 b ofthe molding die 8, and the dies are clamped in a state in which theplurality of device regions are covered with one cavity 8 c of an upperdie 8 a of the molding die 8. As shown in a partially enlarged diagramof FIG. 38 by the die clamping, the resin molding is carried out bymaking the mounted surface 1 d of the lead 1 a intruding into the film11. Consequently, a batch sealing portion 14 is formed so that themounted faces 1 d of the plurality of leads 1 a are exposed to andarranged on the peripheral portion of the rear surface 3 a.

Note that since the end heavy-walled portions shown in FIG. 19 areformed on both ends located in the lead-width direction of the concaveportion 1 m in the lead 1 a, the strength of the lead 1 a can be ensuredand it is possible to prevent occasion of the drawback that the lead 1 ais deformed due to a reaction force occurring at a time of clamping themolding die 8.

After the molding, a soldered layer 6 is formed on the mounted surface 1d of the lead 1 a by performing the external plating in step S15.

Thereafter, a desired mark is attached to a position corresponding tothe sealing portion 3 of each QFN 9 by the marking in step S16.

Then, the QFN 9 is divided to individual pieces by cutting in step S17.

At this time, in this step, each lead 1 a and the batch sealing portion14 are cut out by the dicing to be separated from the lead frame 1. Thatis, each lead 1 a and the batch sealing portion 14 are cut out using ablade 12, whereby separation to individual pieces is carried out.

Note that in the cutting by the dicing using the blade 12, since thestress applied to the lead 1 a is smaller at a time of the lead cuttingthan at a time of the cutting by a punch, damages to the wire bondingportion are also small and drawbacks such as wire peeling and wirecutting can be prevented from occurring.

Then, the cutting of the lead is finished, and products of the QFNs 9shown in step S18 are completed.

Third Embodiment

In a third embodiment, a structure for enhancing a heat-radiationproperty in a semiconductor device having a QFN structure will bedescribed. That is, the QFN 5 described in the first embodiment isformed so that the length (M) between the inner ends 1 h of thesealing-portion forming surfaces 1 g of the leads 1 a disposed to opposeto each other is longer than the length (L) between the inner ends 1 hof the mounted surfaces 1 d, that is, “the length (M)”>“the length (L)”is formed. Consequently, it is possible to expand the chip loadingregion surrounded by the inner end 1 h of the sealing-portion formingsurface 1 g of each lead 1 a and to increase the mountable chip sizewithout changing the package size. However, in such a semiconductordevice, as shown in FIGS. 39 and 41, the QFN 15 of the third embodimentis such that there is mounted the semiconductor chip 2 having such largesize that the chip end approaches each lead 1 a.

In this case, as the semiconductor chip 2 becomes large in size, theheat-radiation property of the chip is required to be improved.Therefore, there is required a structure for exposing the tab 1 b fromthe rear surface 3 a of the sealing portion 3 and for increasing thesize of the tab 1 b up to substantially the same size as thesemiconductor chip 2.

In the QFN 15 shown in FIGS. 39 and 40, by adopting the tab 1 b slightlylarger in size than the semiconductor chip 2, this tab 1 b is exposed tothe rear surface 3 a of the sealing portion 3 and consequently theheat-radiation property of the QFN 15 can be improved.

Also, in the QFN 15 shown in FIGS. 41 and 42, the tab 1 b slightlysmaller in size than the semiconductor chip 2 is adopted, and this tab 1b is exposed to the rear surface 3 a of the sealing portion 3, so thatthe heat-radiation property of the QFN 15 can be improved.

Note that, as shown in a partially enlarged diagram of FIG. 43, in thecase of the QFN 15 having a structure in which the semiconductor chip 2is overhung outside the tab 1 b, the length (overhung length: R)projecting from the end portion of the tab 1 b of the semiconductor chip2 is preferably is equal to or less than the length (S) of the mountedsurface 1 d of the lead 1 a with respect to a lead extending direction.That is, it is desired to form “(R≦(S)”.

For this reason, the length projecting from the end portion of the tab 1b of the semiconductor chip 2 can be suppressed and consequently therecan be provided a gap (T) between the end portion of the chip and theinner end 1 h of the lead 1 a. Therefore, at the time of the resinmolding, the sealing resin can be made to intrude also around and intothe side surface of the tab 1 b on a side of the rear surface 2 c of thesemiconductor chip 2, whereby voids can be prevented from being formedon the side surface of the tab 1 b.

Fourth Embodiment

A fourth embodiment is a technique for further downsizing the size of asemiconductor device having a QFN structure, and is mainly asemiconductor device in which stabilization of a fixed potential such asa GND potential is achieved. In this case, a QFN 16 having asemiconductor chip 2 in which a circuit operated by high frequency isincorporated will be described as an example.

The QFN 5 shown in FIG. 2 and described in the first embodiment isformed so that the length (M) between the inner ends 1 h of thesealing-portion forming surfaces 1 g of the leads 1 a disposed to opposeto each other becomes longer than the length (L) between the inner ends1 h of the mounted surfaces 1 d and consequently the chip mountingregion surrounded by the inner end 1 h of the sealing-portion formingsurface 1 g of each lead 1 a can be expanded and enlargement of the sizeof the mountable chip without changing the package size is achieved.However, in such a semiconductor device, the QFN 16 of the fourthembodiment is intended not to increase a common terminal such as a GNDterminal allocated to the lead 1 a but to stabilize a fixed potentialsuch as a GND potential by using a portion of the tab hanging lead 1 eas an external terminal for the common terminal.

Thus, by using the portion of the tab hanging lead 1 e as an externalterminal for GND, a GND lead conventionally allocated to the lead 1 acan be made an empty lead and hence the size of the semiconductor devicecan be reduced by decreasing the number of leads.

The QFN 16 shown in FIGS. 44 and 45 is formed so that the length (M)between the inner ends 1 h of the sealing-portion forming surfaces 1 gof leads 1 a disposed so as to oppose to each other is larger than thelength (L) between the inner ends 1 h of the mounted surfaces 1 dsimilarly to the QFN 5 shown in FIG. 2. Consequently, the chip mountableregion surrounded by the inner end 1 h of the sealing-portion formingsurface 1 g of each lead 1 a can be expanded, and concurrently theconductive wire 4, whose one end is connected to the pad 2 a of thesemiconductor chip 2, is such that the other end is connected to aregion opposing to the above-mentioned mounted surface 1 n of an uppersurface 1 q that is an opposite surface to the mounted surface 1 n ofthe tab hanging lead (hanging lead) 1 e.

That is, the pad 2 a for GND of the semiconductor chip 2 is connected tothe tab hanging lead 1 e through the wire 4, and since the four tabhanging leads 1 e are respectively linked to the tab 1 b, the four tabhanging leads 1 e are used as a common external terminal for GND.

At this time, a connecting position of the wire 4 to the tab hanginglead 1 e is an upper surface 1 g opposing to the mounted surface 1 n ofan exposed portion 1 p of the tab hanging lead 1 e.

That is, as shown in FIG. 45, the wire 4 is connected to a portion whichis not eccentric in a thickness direction of the tab hanging lead 1 e(e.g., a portion not subjected to a process such as change in thicknessor bending). In the QFN 16 shown in FIG. 45, the tab 1 b and the tabhanging lead 1 e are partially half-etched and the wire 4 is connectedto the exposed portion 1 p in which the thickness of the tab hanginglead 1 e is not changed.

Note that the wire bonding to the tab hanging lead 1 e is preferablyperformed at as outside a position of the tab hanging lead 1 e aspossible in order to improve the stability thereof at the time of thewire bonding. This is for securely making a heat block used at the timeof the wire bonding contact closely with the exposed portion 1 p.Thereby, heat or ultrasonic wave generated at the time of the wirebonding is securely transmitted from the exposed portions 1 p of the tabhanging lead 1 e and so the wire bonding to the tab hanging lead 1 e canbe stabilized.

Further, since it is easily possible to make the semiconductor chip 2large in size, the wire bonding to the tab hanging lead 1 e ispreferably carried out at as outside a position of the tab hanging lead1 e as possible.

Also, a concave portion 1 r, which is a slit, is formed outside theconnecting position of the wire 4 in the upper surface 1 q of theexposed portion 1 p of the tab hanging lead 1 e of the QFN 16. In thecase where the lead cutting is performed in the structure obtained afterthe resin molding and shown in FIGS. 46 and 47, the above-mentionedconcave portion 1 r relaxes the stress applied to the connectingposition of the wire 4 on the tab hanging lead 1 e at a time of thecutting by tearing of the tab hanging lead 1 e.

That is, the cutting by tearing of the tab hanging lead 1 e is carriedout so as to apply a rotational stress to the notch portion 1 u of thetab hanging lead 1 e as shown in FIG. 47 and tear 1 t. At this time, thestress in the lead-thickness direction at the time of the cutting isconcentrated to the concave portion 1 r so that the stress due to thecutting is not applied to the connecting position of the wire 4.Consequently, wire peeling can be prevented from occurring at the timeof cutting the tab hanging lead 1 e.

Further, when a leak path on the tab hanging lead 1 e can be lengthenedby the concave portion 1 r, an amount of water invading along the tabhanging lead 1 e can be reduced.

Also, projecting portions is are provided in both side surfaces locatedoutside a position to which the wire 4 of the exposed portion 1 p of thetab hanging lead 1 e is connected. This projecting portion is relaxesthe stress applied to the connecting position of the wire 4 on the tabhanging lead 1 e at the time of the cutting by tearing of the tabhanging lead 1 e similarly to the concave portion 1 r, and furtherrelaxes a stress exerted in a lead-horizontal direction at the time ofcutting the tab hanging lead 1 e. That is, when the tab hanging lead 1 eis cut out, this projecting portion is receives the stress caused by thecutting in the lead-horizontal direction so that the stress by thecutting is not applied to the connecting position of the wire 4.

Further, the leak path on the tab hanging lead 1 e can be lengthenedeven by this projecting portion 1 s, and an amount of water invadingalong the tab hanging lead 1 e can be reduced.

Also, as shown in a QFN 16 of a modified example in FIGS. 50 and 51,another concave portion 1 t may be further formed inside the connectingposition of the wire 4 on the upper surface 1 q of the exposed portion 1p of the tab hanging lead 1 e. The concave portion 1 t formed inside theconnecting position of the wire 4 is intended to absorb a heat stress atthe time of conducting a reliability test (temperature cycle test) in astate in which the QFN 16 is mounted on a mounting substrate 17 (seeFIG. 53), and thereby can prevent the heat stress from being applied tothe connecting position of the wire 4 at the time of the reliabilitytest.

Note that in the QFN 16 of the fourth embodiment, so as not to decreasethe number of leads 1 a in using the tab hanging lead 1 e as an externalterminal for GND, each of chamfered portions 3 c at four corners on therear surface 3 a of the sealing portion 3 is disposed in the mountedsurface 1 n of the exposed portion 1 p of the tab hanging lead 1 e.

That is, in the semiconductor device having the original QFN structure,since the tab hanging leads 1 e are disposed on the corners of thesealing portion 3, the mounted surfaces 1 n of the exposed portions 1 pof the tab hanging leads 1 e are disposed on the corners of the sealingportion 3 by using the above arrangement and each of the mountedsurfaces 1 n is used as an external terminal for GND. Therefore, it isunnecessary to decrease the number of leads 1 a. In other words, byusing the tab hanging lead 1 e as an external terminal for GND, the leadfor GND conventionally allocated to the lead 1 a can be made an emptylead, and hence the semiconductor device can be downsized by reducingthe number of leads.

Consequently, a mounting area of the QFN 16 can be reduced.

Also, a QFN 16 of a modified example shown in FIGS. 48 and 49 has astructure in which a tab raising process is performed so that theposition of the tab 1 b is higher than that of the lead 1 a, andconsequently becomes a tab embedding structure in which the tab 1 b issealed by the sealing portion 3. Note that the QFN 16 shown in FIGS. 44and 45 is such that the rear surface 1 l of the tab 1 b is formed thinby half etching and, also in this case, the QFN becomes a tab embeddingstructure in which the tab 1 b is sealed by the sealing portion 3.

by adopting such a tab embedding structure, since the tab 1 b is notexposed to the rear surface 3 a of the sealing portion 3, the wire canbe led around a region located below the tab 1 b when the QFN ismounted, so that a degree of freedom of leading the wires around themounting substrate 17 can be improved.

Next, an arrangement relation between the external terminal (lead 1 aand tab hanging lead 1 e) at the time of the QFN mounting and theterminal 17 a of the mounting substrate 17 will be described.

Firstly, as shown in FIG. 52, the length (U) of the mounted surface 1 nin the lead extending direction in the exposed portion 1 p of the tabhanging lead 1 e is preferably larger than the thickness of the exposedportion 1 p of the tab hanging lead 1 e. As an example, when thethickness (thickness of lead frame) of the exposed portion 1 p is 0.2mm, U=0.55 mm. At this time, the thickness and length (U) of the exposedportion 1 p are not limited to these values.

Thus, by increasing the length (U) of the exposed portion 1 p of the tabhanging lead 1 e, since a connecting area with the terminal 17 a of theloading substrate 17 increases, the heat-radiation property of the QFN16 can be improved.

In this case, in a region outside the mounted surface 1 n of the exposedportion 1 p of the tab hanging lead 1 e, a shortest-distance portionbetween the leads 1 a adjacent to each other is sealed by the sealingportion 3. That is, in view of a heat-radiation property, the mountedsurface 1 n of the exposed portion 1 p is preferably extended inward.However, it is necessary to take care of solder leaks because theadjacent leads 1 a are disposed on both sides of the tab hanging lead 1e, as shown in FIG. 52.

Therefore, since the shortest-distance portion between the adjacentleads 1 a in the region located inside the mounted surface 1 n of thetab hanging lead 1 e is sealed by the sealing portion 3, the solderleaks can be prevented at the time of the mounting onto the mountingsubstrate 17.

Further, as shown in FIG. 53, the terminal 17 a of the mountingsubstrate 17 connected to the lead 1 a adjacent to the tab hanging lead1 e is preferably disposed so that its inner end 17 b coincides planarlywith or is outside the inner end 1 h of the mounted surface 1 d of thelead 1 a.

That is, in mounting the QFN 16 on the mounting substrate 17, the innerend 17 b of the terminal 17 a of the mounting substrate 17 is disposedso as to coincide planarly with or be outside the inner end 1 h of themounted surface 1 d of the corresponding lead 1 a. Therefore, theterminal 17 a of the mounting substrate 17 can be prevented fromapproaching to such an extent that it contacts with the exposed portion1 p of the lead 1 e, whereby the solder leaks occurring in the mountingsubstrate 17 at the time of the mounting can be prevented.

Next, an electric characteristic inspection of the QFN 16 of thisembodiment will be described.

FIGS. 54 and 55 are views showing an electric characteristic inspectionfor the QFN 16. At a time of the inspection, as shown in FIGS. 56 and57, the QFN 16 is disposed at a positioning base 18 c of a main body 18a of a socket 18 and then, and a lid portion 18 b is closed and the QFN16 is pressed by a package holder 18 d to attach the QFN 16 to thesocket 18.

Consequently, as shown in FIG. 55, since a contact pin 18 e contactswith the mounted surface in of the exposed portion 1 p of the tabhanging lead 1 e, the electric characteristic inspection can be made.

At this time, as shown in FIG. 58, tests are conducted in states inwhich the GND potential is supplied to a “A circuit” for high frequencythrough the pad 2 a and a high-frequency amplifier 2 d from theindependent tab lead 1 e for GND and further in which the GND potentialis supplied to the “A circuit” for high frequency through the pad 2 aand the high-frequency amplifier 2 d from the exposed portion 1 p of thetab hanging lead 1 e, which is a common terminal.

Thus, the GND potential is stabilized by supplying sufficiently the GNDpotential and the tests is conducted under the condition in which thehigh-frequency characteristic of the “A circuit” is ensured, so that thehigh-frequency characteristic of the semiconductor chip 2 can beimproved. That is, characteristics of the high-frequency “A circuit” canbe tested under circumstances near a state of being actually used as aproduct.

Note that at the time of mounting the QFN 16 on the socket 18, sincecontact pins 18 e for signal also contact respectively with the leads 1a for signal, the desired electric characteristic inspection is carriedout by inputting an electric signal through a predetermined lead 1 a asoccasion demands.

Fifth Embodiment

FIG. 59 shows a structure of a QFN 19 according to a fifth embodiment.In the QFN 19, the wire 4 is connected to the tab hanging lead 1 e, buteach lead 1 a is such that the relation between the length (P) of themounted surface 1 d and the length (Q) of the sealing-portion formingsurface 1 g as shown FIG. 2 is not “P>Q” but “P=Q”.

That is, the GFN 19 has the structure in which the length of the mountedsurface 1 d is equal to that of the sealing-portion forming surface 1 g.

Even in the QFN 19 having such a structure, the same effects as those ofthe QFN 16 of the fourth embodiment can be obtained by a technique forconnecting the wire 4 to the tab hanging lead 1 e or/and a technique forproviding the concave portions 1 r and 1 t and the projecting portion 1s to the tab hanging lead 1 e.

In the foregoing description, the invention made by the presentinventors has been specifically described based on the embodiments.However, needless to say, the present invention is not limited to theabove-mentioned embodiments and can be variously modified and alteredwithout departing from the gist thereof.

For example, in the first embodiment, the case where the QFN 5 isassembled using the lead frame 1 in which the plurality of packageregions (regions surrounded by the cutting portion 1 j) as shown in FIG.7 are formed in matrix arrangement has been described. However, theassembly of the semiconductor device (QFN 5) may be carried out usingthe stripe-shaped multiple lead frame 1 in which two or more of theabove-mentioned package regions are formed in line.

Also, the technique for relaxing the stress applied to the connectingposition of the wire 4 by providing the tab hanging lead 1 e describedin the fourth embodiment with the concave portions 1 r and 1 t and/orthe projecting portion 1 s is not limited to the semiconductor devicehaving the QFN structure, and may be a semiconductor device in which theleads 1 a extend in two directions opposed to each other if thesemiconductor device is of a non-lead type.

INDUSTRIAL APPLICABILITY

As described above, the semiconductor device of the present invention ispreferably applied to the non-lead type semiconductor device in whicheach lead is exposed partially to and disposed on the end portion of therear surface of the sealing portion, and particularly is preferableapplied to a QFN in which the leads extend in four directions.

1. A semiconductor device comprising: a plurality of leads each having asealing surface, a mounting surface opposite to said sealing surface, aninner surface disposed between said sealing surface and said mountingsurface, an outer surface disposed between said sealing surface and saidmounting surface and opposite to said inner surface, and a plurality ofside surfaces each disposed between said sealing surface and saidmounting surface and between said inner surface and said outer surface;a chip mounting portion having a chip supporting surface and a backsurface opposite to said chip supporting surface, and arranged betweensaid leads in a plan view; a semiconductor chip having a front surface,a plurality of electrodes formed on said front surface, and rear surfaceopposite to said front surface, and mounted on said chip supportingsurface of said chip mounting portion; a plurality of wires electricallyconnecting said electrodes with said leads, respectively; and a sealingmember having an upper surface, a lower surface opposite to said uppersurface, and a plurality of side surfaces disposed between said uppersurface and said lower surface, and sealing said semiconductor chip,said leads and said wires such that said mounting surface of each ofsaid leads is exposed from said lower surface of said sealing member andsuch that a part of said sealing member contacts with said rear surfaceof said semiconductor chip; wherein said inner surface of each of saidleads faces said chip mounting portion; wherein each of said leads has afirst inner end portion at an intersection of said sealing surface withsaid inner surface, and a second inner end portion at an intersection ofsaid mounting surface with said inner surface; wherein said second innerend portion is closer to said chip mounting portion than said firstinner end portion in said plan view; and wherein a width of said sealingsurface in a intersecting direction intersecting with a respectiveextending direction of each of said leads is wider than that of saidmounting surface in said intersecting direction.
 2. The semiconductordevice according to claim 1, wherein a recess is formed on said sealingsurface.
 3. The semiconductor device according to claim 1, wherein eachsaid side surface of each said lead has a curved portion.
 4. Thesemiconductor device according to claim 1, wherein said outer surface ofeach said lead is exposed from said side surface of said sealing member.5. The semiconductor device according to claim 1, wherein a dimension inthe plan view of said chip mounting portion is smaller than that of saidsemiconductor chip.
 6. The semiconductor device according to claim 1,wherein said back surface of said chip mounting portion is exposed fromsaid lower surface of said sealing member.
 7. The semiconductor deviceaccording to claim 1, wherein a thickness of said chip mounting portionis less than that of each said lead; and wherein said back surface ofsaid chip mounting portion is covered with said sealing member.